MALDI-MS using UV wavelength laser irradiation has become a widely adopted technique for biological applications that require MW determination of peptides and proteins. IR wavelength laser irradiation has been much less used for MALDI-MS applications. One reason for the small amount of research in IR MALDI has been the lack of a convenient commercial IR-wavelength laser that produces pulses of short duration. All studies to date carried out using Er(YAG) lasers with a fixed wavelength of 2.94 (m and pulse duration in the range 100 - 200 ns. The recent commercial availability of optical parametric oscillators (OPO) that allow ready tuning of the laser wavelength in the range 0.7 - 4.0 (m and intense pulses of irradiation with duration ( 6 ns has made it attractive for us to plan a thorough re-investigation of IR MALDI. This investigation of IR MALDI is being undertaken using a Surelite II Nd(YAG) pump laser in combination with a Mirage 3000 OPO (Continuum, Santa Clara, CA .). cont.. We have successfully coupled the output of the OPO to our second custom built MALDI-TOF instrument and have carried out an extensive program of research with the new instrument. We have made a number of interesting findings that are reported in a paper (S. Niu, W. Zhang, and B.T. Chait "Direct Comparison of Infrared aand Ultraviolet Wavelength Matrix-Assisted Laser Desorption Mass Spectrometry of Proteins" J. Am. Soc. Mass Spectrom. 9, (1998) 1-7). These findings are of potential value both from a practical and a fundamental point of view (for obtaining an understanding of the MALD-MS process).